There are many situations in which it is desirable to clean surfaces of scale, corrosion, or contaminant buildup, in high temperature environments. For example, in the petrochemical industry, "white metal cleaning" (that is cleaning the metal so that it is free of scale and other buildup) is often desirable, as is cleaning of reheat tubes, or any metal surfaces where scale buildup may impede the thermal transferability of the metal surface. Also, in a number of different conventional furnaces, cleaning of the furnace walls, ceiling, and possibly even floor, is occasionally desirable.
In the past it has been difficult to properly effect cleaning in high temperature environments in a time and cost efficient manner. Typical commercial operations can only direct a blasting media against the high temperature surfaces that require cleaning at operating temperature or in situ for only a few minutes. Otherwise the equipment utilized to effect cleaning is compromised. Therefore, it is necessary to blast for a few minutes, remove the equipment, and subsequently reintroduce it, until ultimately the cleaning operation is substantially complete. Using conventional commercial techniques, it is also difficult to effect cleaning of all of the surfaces that need cleaning without constantly moving equipment from place to place since typically equipment is limited to cleaning 5 or 15 feet from the equipment location. Also, typically inorganic blasting media, such as sand, glass beads, or the like, are utilized in some environments, which causes a buildup on the floor or lower surface surrounding the areas being cleaned, necessitating the removal of the blasting media.
According to the present invention a method is provided which overcomes the problems of the prior art commercial installations discussed above. According to the present invention, it is possible to clean high temperature surfaces even while the equipment is in operation, or at least in situ and still at high temperature, for essentially continuously as long as necessary in order to properly effect cleaning. Also cleaning may be effected at locations within a furnace or other installation to be cleaned up to 40 feet (or even more) without requiring removal of the equipment, and in some circumstances areas can be reached that cannot practically be reached by any commercial technique (although there may be a need to employ several lances, of different and irregular shapes, in a particular furnace to practice the invention).
Also, the invention can be practiced with a blasting media that combusts at the high temperature in the high temperature environment where cleaning is being effected, such as by using primarily or substantially exclusively organic blasting media, such as walnut shells. Walnut shells, and other agricultural particles such as peach or apricot stone particles, corn cob particles, and the like, are well known as media for cleaning aluminum or other metal surfaces of paint or corrosion, and for mass deburring and finishing of small components utilizing tumbling barrels or vibratory cleaners. However, use as a blasting media in high temperature environments over extended time periods has not heretofore been practical. However, such media may be used practically in a highly advantageous manner according to the method of the present invention.
It is possible to practice the method according to the present invention by utilizing a standard piece of equipment well known in another art. In the art of ceramic welding (such as discussed generally in U.S. Pat. Nos. 5,100,594 and 5,378,493, the disclosures of which are hereby incorporated by reference herein), equipment known as a liquid-cooled welding lance is typically used to apply a particulate material that is used to patch up furnace surfaces of refractory material. While these welding lances may have a number of configurations, typically they include single or double cooled liquid (typically water) circulating tubes surrounding a welding particulate material center tube. The welding lances are typically made out of steel or like corrosion and temperature resistant material, and steel spacers are typically provided spacing the various tubular elements from each other. Utilizing these welding lances, high temperature repairs of refractory surfaces of furnaces are practiced while the furnaces are at operating temperature, and substantially continuously without the need to reposition the lances from place to place and attempted access to the furnace to be repaired at different locations. These welding lances, such as used by Fosbel, Inc. of Berea, Ohio, and other companies of the Fosbel Group, can access locations easily up to 40 feet (and perhaps more) within a furnace to be repaired.
According to the present invention, the liquid-cooled welding lances that are typically used for ceramic welding are used for effecting cleaning of surfaces that have scale, corrosion, or other contaminant buildups thereon. By practicing the invention it is possible to effectively clean the surfaces in a time and cost efficient manner, without destroying the surfaces, and with a minimum of practical difficulty. Conventional liquid cooled welding lances are easily modified to practice the invention since it is merely a matter of utilizing a different media, and perhaps different pressures and details of movements of the lances, for introduction into an area to be treated. Also the owner of the equipment being treated will get increased production because the furnace need not be shut down to practice the invention, and there is no need to lower the temperature of the furnace to ensure no damage to equipment, as is typically necessary with other technologies.
According to one aspect of the invention, a method of cleaning surfaces at high temperature using a liquid-cooled lance (a conventional lance for ceramic welding) is provided comprising: (a) While the surfaces are at a temperature of 400 degrees F or more, positioning the liquid-cooled lance in operative association with the surfaces. (b) Introducing particulate blasting media through the lance under super-atmospheric pressure so that the blasting media impacts the surfaces and cleans them while the surfaces are at a temperature of 400 degrees F or more. And (c) continuing (b), without the necessity of removing the lance to a location remote from operative positioning with respect to the surfaces, until the surfaces are substantially cleaned. Of course depending upon the surfaces to be cleaned (a)-(c) may be practiced while the surfaces are at a temperature of more than 1000.degree. F. (or more than every other temperature between 400 and 1000.degree. F.); in fact there is almost no limit, from the practical standpoint, of the temperature of the surfaces to be cleaned since the liquid cooled lances can be designed with extra cooling capacity, double sleeves, or the like, so as to be useful in almost any normal industrial environment. While the invention of the method is practical in almost any industrial situation where high temperature cleaning is desirable, such as in the petrochemical art, typically (a)-(c) are practiced to clean, while in operation or in situ, metal surfaces having scale buildup which adversely affects the ability of the metal surfaces to transfer heat, reheat tubes (i.e. process tubes), or furnace surfaces; or to practice scale/oxide removal of any sort.
In the preferred embodiment of the invention, (b) is practiced using a blasting media that combusts at a temperature of the environment surrounding the surfaces to be cleaned, so that after impacting the surfaces the blasting media will not build up significantly in the environment. For example, (b) may be practiced using one or more organic agricultural abrasive materials (such as pecan, acorn, coconut, or almond shells, peach, apricot, cherry, or plum pits, or even some organic seeds such as olive and prune seeds) as the primary or substantially sole constituent of the blasting media. However, the preferred blasting media is primarily or substantially solely walnut shells, most desirably black walnut shells. Black walnut shells typically have an average hardness of about 2.5-3 moh and a modulus of elasticity of 175,000 psi. Step (b) is preferably practiced using blasting media having an average hardness of between about 2-4 moh, a modulus of elasticity greater than 75,000 psi, and an average particle size of between about 10-100 mesh, e.g. 30-60 mesh, but dependent upon the particular surfaces to be cleaned.
Other materials, such as plastic blast media ("PMB"), may be utilized as the blasting media, or part of the blasting media mixed with walnut shells or other organic material. There are typically three types of PMB, polyester (3.0 moh), urea formaldehyde (3.5 moh), and melamine formaldehyde (4.0 moh). Often blasting media with a hardness much higher than 4 moh, or some types of plastic, may have adverse environmental consequences (as evaluated by the EPA, OHSA, DOT, or like agencies), or contaminate the area being cleaned, and should usually be avoided. Therefore, if universal applicability of the blasting media is a desired feature, then a hardness of about 4 moh or less, while still capable of performing effective cleaning, without buildup or adverse environmental consequences, is desirable.
In the above described method (b) may be practiced by directing the blasting media at the surfaces at a pressure of about 40-100 psi. While the pressure will depend upon the particular surfaces involved and the blasting media utilized, for black walnut shells, the desired value is between about 40-100 psi, e.g. about 80 psi. The method of the invention allows (c) to be practiced substantially continuously virtually indefinitely, but certainly for more than thirty minutes (e.g. 45-180 minutes) without any need to remove the lance from the high temperature environment since the lance readily resists the high temperature of the environment. Also, because the lance may easily be made to operating lengths of 40 feet, or even more, in almost all practical situations the equipment may be positioned only once to effect complete cleaning of the desired surfaces of any particular installation.
The other equipment utilized in the practice of the invention, such as the cooling water circulating equipment, and the media introduction equipment, are also the same conventional equipment as used for ceramic welding, such as by Fosbel, Inc. The same types of pumps for circulating the cooling liquid and for pressurizing the media introduced for ceramic welding applications are suitable for the cleaning method according to the invention.
According to another aspect of the present invention a method of cleaning surfaces at high temperature using a liquid cooled lance is provided comprising: (a) While the surfaces are at a temperature of 400 degrees F or more, positioning the liquid-cooled lance in operative association with the surfaces. And (b) introducing particulate blasting media through the lance under super-atmospheric pressure so that the blasting media impacts the surfaces and cleans the surfaces while the surfaces are at a temperature of 400 degrees F or more; and wherein (b) is practiced using a blasting media that combusts at the temperature of the environment surrounding the surfaces to be cleaned, so that after impacting the surfaces the blasting media will not build up significantly in the environment.
In this aspect of the method, (b) is preferably practiced using one or more organic agricultural abrasive materials as the primary constituent of the blasting media, and by directing the media at the surfaces at a pressure of between 40-100 psi, e.g. by using black walnut shells as substantially the sole constituent of the blasting media. In any event preferably (b) may be practiced by using a blasting media having an average hardness of between about 2.5-4 moh, and having an average particle size of between about 10-100 mesh. Also, typically (a) and (b) are practiced substantially continuously for at least thirty minutes.
According to yet another aspect of the present invention there is provided a method of cleaning a surface at a temperature of 1000.degree. F. or more by directing substantially continuously for at least 15 minutes a substantially combustible, particulate blasting media comprising primarily, or substantially solely, black walnut shells, under super-atmospheric pressure against the surface to be cleaned so that the blasting media impacts the surface and effects abrasive cleaning thereof, and then combusts.
It is the primary object of the present invention to provide a time and cost efficient method for the cleaning of high temperature surfaces, such as in the petrochemical industry, furnaces, and the like. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.